A communication system transmits frames with an arbitrary information length among a plurality of possible information lengths. On receipt of a frame, a receiver performs Viterbi decoding and a CRC operation assuming that the information length of the relavent frame is the same as that of an immediately previous frame. The information length of the frame is detected based on the result of the CRC operation.
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16. A method for detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
generating a candidate value which for an information length of a relevant frame based on an information length of a frame received before;
performing error detection process on the relevant frame firstly using the generated candidate value; and
detecting the information length of the relevant frame based on the result of the error detection process.
1. A method for detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
generating a predicted value which predicts an information length of a relevant frame based on an information length of a frame received before;
performing an error detection process on the relevant frame using the generated predicted value; and
detecting the information length of the relevant frame based on the result of the error detection process.
17. A method for detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
selecting a candidate value which for an information length of a relevant frame from among a plurality of candidates based on an information length of a frame received before;
performing error detection process on the relevant frame firstly using the selected candidate value; and
detecting the information length of the relevant frame based on the result of the error detection process.
18. A method for specifying an information length of a received transmission frame by performing an error detection process sequentially using a plurality of information length candidates in a communication system where an information length of a transmission frame is variable, wherein
an order of the plurality of information length candidates used in the error detection process for a following received transmission frame is changed at a receiving side based on a specifying result of information length for the previously received transmission frame.
6. A method for detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
detecting an information length of each of a plurality of frames;
checking a detected frequency for each information length;
performing an error detection process assuming that information with one of the detected information length is stored in a relevant frame according to the detected frequencies; and
detecting an information length of the relevant frame based on a result of the error detection process.
20. An apparatus to detect an information length of a frame in a communication system which transmits frames storing information, said apparatus comprising:
means for selecting a candidate value for an information length of a relevant frame from among a plurality of candidates based on an information length of a frame received before;
means for performing error detection process on the relevant frame firstly using the selected candidate value; and
means for detecting the information length of the relevant frame based on the result of the error detection process.
21. An apparatus to specify an information length of a received transmission frame by performing an error detection process sequentially using a plurality of information length candidates in a communication system where the information length of a transmission frame is variable, said apparatus comprising:
means for changing an order of the plurality of information length candidates used in an error detection process for a following a received transmission frame at a receiving side based on a specifying result of information length for the previously received transmission frame.
19. An apparatus to detect information length of a frame in a communication system, said communication system transmitting frames storing information, said apparatus comprising:
a generator unit generating a candidate value for an information length of a relevant frame based on an information length of a previously received frame received;
an error detector performing error detection process on the relevant frame firstly using the generated candidate value; and
an information length detector detecting the information length of the relevant frame based on the result of the error detection process.
13. A detection device detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
a receiving unit receiving the frame;
a predicting unit generating a predicted value which predicts an information length of a relevant frame based on an information length of a frame received before by said receiving unit; an error detector performing an error detection process on the relevant frame using the predicted value generated by said predicting unit; and
an information length detector detecting an information length of the relevant frame based on the detection result of said error detector.
10. A detection device detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
receiving means for receiving the frame;
predicting means for the generating a predicted value which predicts an information length of a relevant frame based on an information length of a frame received before the said receiving means;
the error detecting means for performing an error detection process on the relevant frame using the predicted value generated by said predicting means; and
information length detecting means for detecting an information length of the relevant frame based on the detection result of said error detecting means.
14. A detection device for detecting an information length of a frame in a communication system which transmits frames storing information, comprising:
a receiving unit receiving a transmission frame;
an extracting unit extracting a data string from the transmission frame received by said receiving unit;
an error detector performing an error detection process on the data string extracted by said extracting unit; and
an information amount detector detecting the amount of information stored in the transmission frame based on the detection result of said error detector, wherein
said extracting unit determines the number of bits of data string to be extracted from the transmission frame based on a detection result by said information amount detector.
11. A detection device for detecting an information length of frame in a communication system which transmits frames storing information, comprising
receiving means for receiving a transmission frame;
extracting means for extracting a data string from the transmission frame received by said receiving means;
error detecting means for performing an error detection process on the data string extracted by said extracting means; and
information amount detecting means for detecting the amount of information stored in the transmission frame based on the detection result of said error detecting means, wherein
said extracting means determines the number of bits of data string to be extracted from the transmission frame based on a detection result by said information amount detecting means.
15. A detection device detecting a transmission format of information stored in a frame in a communication system which transmits frames storing information with an arbitrary transmission format among a plurality of transmission formats, comprising:
a receiving unit receiving the frame;
the transmission format of information stored in the relevant frame based on the transmission format of information stored in a frame received before by said receiving unit;
an error detector performing an error detection process on the information stored in the relevant frame assuming that the transmission format of the information coincides with the predicted transmission format predicted by said prediction unit; and
a format detector detecting the transmission format of information stored in the relevant frame based on the detection result of said error detector.
12. A detection device detecting a transmission format of information stored in a frame in a communication system which transmits frames storing information with an arbitrary transmission format among a plurality of transmission formats, comprising:
receiving means for receiving the frame;
predicting means for predicting the transmission format of information stored in the relevant frame based on the transmission format of information stored in a frame received before said receiving means;
error detecting means for performing an error detection process on the information stored in the relevant frame assuming that the transmission format of the information coincides with the predicted transmission format predicted by said prediction means; and
format detecting means for detecting the transmission format of information stored in the relevant frame based on the detection result of said error detection means.
2. The method according to
3. The method according to
4. The method according to
5. The method according to
7. The method according to
the error detection process is performed assuming that an information length of the relevant frame coincides with a corresponding detected information length in descending order of the detected frequencies, when an error detection process detects an error in the relevant frame.
8. The method according to
checks a transmission frequency for each information length, and
stores in a frame information with an information length with the greatest transmission frequency with priority and transmits the frame.
9. The method according to
stores in a frame information with the same information length as an information le of a frame transmitted immediately before, and transmits the frame, and
stores in a frame information with the information length with the greatest transmission frequency with priority and transmits the frame, when information with the same information length as the information length of the frame transmitted immediately before cannot be transmitted.
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This application is a continuation of an international application of PCT/JP00/04059, which was filed on Jun. 21, 2000.
1. Field of the Invention
The present invention relates to a communication system in which the amount (number of bits or length) of information stored in a transmission frame can dynamically vary for each transmission frame.
2. Description of the Related Art
Recently, mobile communications have rapidly spread and a variety of communication methods have been proposed and developed. One next-generation cellular phone system (IMT-2000), W-CDMA (Wideband-Code Division Multiplex Access) is proposed.
In W-CDMA, a variety of new technologies are introduced to facilitate a high transferrate, increasing number of users, effective use of the radio band. A technology called “BTFD (Blind Transport Format Detection)” is one such newly-adopted technology.
A system adopting BTFD can dynamically change the data rate while transmitting information. Specifically, while information is stored in a frame and transmitted, the number of information bits (that is to say, information length) in a frame can be changed for each frame. In this case, a transmitter does not notify a receiver of the information length of a frame. Therefore, when obtaining information from a received frame, the receiver must detect the information length of the frame.
In this way, in BTFD, the information length of each radio frame can be changed for each frame. Then, the receiver detects the information length on receipt of the transmitted information.
On receiving a signal (radio frame) in step S1, the process for detecting the information length of the radio frame is started. In steps S2 and S3, error detection is performed assuming that the information length of the received radio frame is 50 bits. This error detection is, for example, a CRC operation. In step S3, if no error is detected, it is judged that the information length of the received radio frame is 50 bits, and the 50 bits of information are obtained. If an error is detected in step S3, the flow proceeds to step S4.
In steps S4 and S5, error detection is performed assuming that the information length of the received radio frame is 100 bits. In step S5, if no error is detected, it is judged that the information length of the received radio frame is 100 bits, and the 100 bits of information are obtained. If an error is detected in step S5, the flow proceeds to step S6.
In steps S6 and S7, error detection is performed assuming that the information length of the received radio frame is 200 bits. In step S7, if no error is detected, it is judged that the information length of the received radio frame is 200 bits, and the 200 bits of information are obtained. However, if an error is detected in step S7, it is judged that an error in the transmission line occurs, and a process corresponding to the error is performed in step S8.
In this way, in a communication system adopting BTFD, a receiver detects the information length of a radio frame every time a frame is received and it obtains the information accordingly. As described above, in existing BTFD, when an error detection process with a prediction of an information length of received frame is repeated, the order of the predicted information length used in the error detection process is fixed.
For a detailed description of BTFD, see for example 3rd Generation Partnership Project; Technical Specification Group Radio Access Network, Multiplexing and channel coding (3G TS 25.212 version 3.1.0).
If the algorithm shown in
However, before performing this error detection, generally, error correction decoding, in which the operation amount is large, must be performed. Therefore, if the number of times that the error detection process is performed increases, it requires a longer processing time and a larger amount of power. As a result, it is advantageous to minimize the number of times that the error detection process is performed.
Although in the above example, it is assumed that the system uses three kinds of information lengths, it follows that the average number of executions of the error detection process will increase, as the number of information lengths increase.
The object of the present invention is to reduce the amount of processing needed to detect the amount of information received in a communication system in which the amount of information can vary for each frame. More specifically, the object of the present invention is to reduce the operation amount performed in BTFD applied to W-CDMA and thereby to reduce power consumption.
The transmission format detection method of the present invention detects an information length of a frame in a communication system that transmits frames storing information, comprises; generating a predicted value which predicts an information length of a relevant frame based on an information length of a frame received before; performing an error detection process on the relevant frame using the generated predicted value; and detecting the information length of the relevant frame based on the result of the error detection process.
According to this method, in a communication system having a specific tendency to use a given information length, an error detection process can be efficiently performed by utilizing the previous detection results, and thereby a number of execution of the error detection process is reduced.
In this method, the information length can, for example, be predicted based on the information length of an immediately previous frame. By predicting the information length in this way, the efficiency of an error detection process is improved, when frames with identical information length are consecutively transmitted.
The format detection method, in another aspect of the present invention, detects the information length of a frame in a communication system that transmits frames storing information, comprises; detecting an information length of each of a plurality of frames; checking a detected frequency for each information length; performing an error detection process assuming that information with one of the detected information length is stored in a relevant frame according to the detected frequencies; and detecting an information length of the relevant frame based on a result of the error detection process.
According to this method, the efficiency of error detection is improved, especially in a communication system that frequently transmits frames of a specific information length.
The embodiments of the present invention are described below. First, the basic BTFD algorithm of the present invention is described.
The BTFD algorithm of the present invention predicts the information length of a transmission frame and performs an error detection process based on the prediction. Specifically, a receiver predicts whether the information length of a transmission frame is 50 bits, 100 bits or 200 bits, and performs the error detection process on information with the predicted information length.
In this example, the first, second and third predicted values are used. The first, second and third predicted values are stored in memory areas x(0), x(1) and x(2), respectively. Since in this example, transmission frames can store information with one of three lengths, the first through third predicted values are used. However, if transmission frames can store information with one of N lengths, N predicted values are used.
In step S11, the initial setting of the predicted values are made. In this case, for example, “50 bits”, “100 bits” and “200 bits” are set in the memory areas x(0), x(1) and x(2) as the first, second and third predicted values, respectively.
Then, a signal (transmission frame) is received in step S12, and the first predicted value is extracted from the memory area x(0) in step S13. In this case, the first predicted value is “50 bits”. Therefore, in step S14, an error detection process is performed assuming that 50 bits of information are stored in a prescribed position of the received transmission frame. Then, if no error is detected, it is judged that the information length of the transmission frame coincides with the first predicted value (50 bits). In this case, the flow proceeds to step S20 and Process A is performed. The content of “Process A” is described later. If an error is detected in step S14, it is judged that the information length of the transmission frame does not coincide with the first predicted value, and the flow proceeds to step S15.
In step S15, the second predicted value is extracted from the memory area x(1). In this case, the second predicted value is “100 bits”. Therefore, in step S16, the error detection process is performed assuming that 100 bits of information are stored in the received transmission frame. Then, if no error is detected, it is judged that the information length of the transmission frame coincides with the second predicted value (100 bits), and the flow proceeds to step S20. However, if an error is detected, the flow proceeds to step S17.
Similarly, in step S17, the third predicted value is extracted from the memory area x(2). In this case, the third predicted value is “200 bits”. Therefore, in step S18, the error detection process is performed assuming that 200 bits of information are stored in the received transmission frame. Then, if no error is detected, it is judged that the information length of the transmission frame coincides with the third predicted value (200 bits), and the flow proceeds to step S20. However, if an error is detected, it is judged that some kind of transmission error occurs and the flow proceeds to step S19. In step S19, a signal indicating that the information length of the transmission frame cannot be detected is generated.
In this way, by the processes in steps S13 through S18, the information length of a transmission frame can be detected.
In step S20, process A, the records of the memory areas x(0), x(1) and x(2) are updated with the results of the error detection processes in steps S14, S16 and S18. Specifically, the information length of a received transmission frame is written in the memory area x(0). Here, as described above, the processes in steps S13 through S18 detect the information length of the relevant transmission frame. For example, if no error is detected in step S14, the information length of the transmission frame coincides with the first predicted value. If no error is detected in step S16, the information length of the transmission frame coincides with the second predicted value. Specifically, for example, in a state where “50 bits”, “100 bits” and “200 bits” are set in the memory areas x(0), x(1) and x(2), respectively, and if an error is detected in step S14 and no error is detected in step S16, then it is judged that 100 bits of information are stored in the transmission frame, and “100 bits” is written in the memory area x(0). At this time, either “50 bits” or “200 bits” is written in the memory area x(1), and “200 bits” or “50 bits” is written in the memory area x(2).
In this way, in process A, the information length of a received transmission frame is written in the memory area x(0) as the first predicted value of the next error detection process. Therefore, when a transmission frame is received, the information length of a previous (or immediately previous) transmission frame is set as the first predicted value. In other words, according to the BTFD algorithm of the present invention, when a transmission frame is received, the error detection process is performed using the information length of a previous transmission frame as the predicted value. Then if the prediction fails, the error detection process using another predicted value is performed.
The BTFD algorithm described above is efficient in a communication system where the information length of transmission frames seldom varies or identical information length is often consecutively used. For example, it is assumed that when ten frames are transmitted and information lengths of the frames vary only once. Specifically, it is assumed that five consecutive transmission frames with 50 bits of information are transmitted, and then five consecutive transmission frames with 100 bits of information are transmitted. In this case, when a transmission frame with 50 bits of information is received, “50 bits” is set as the first predicted value. Therefore, during this period, since the information length of the transmission frame coincides with the first predicted value, if there is no transmission error, then it is judged that there is “no error” in step S14 of the flowchart shown in
After these five frames, transmission frames storing 100 bits of information are received. Here, at this time when a first transmission frame storing 100 bits of information is received, “50 bits” is set as the first predicted value. In this case, since the information length of this transmission frame, 100 bits, does not coincide with the first predicted value, 50 bits, therefore, “error” is detected in step S14. Then, following the flowchart, step S16 is executed. In this case, if “100 bits” is set as the second predicted value, then it is judged that there is “no error” in step S16, and the “information length=100” is detected. In this way, when the information lengths of two consecutive transmission frames differ, the error detection process is performed twice. In this example, if “200 bits” and “100 bits” are set as the second and third predicted values, the error detection process is performed three times when receiving the first transmission frame storing 100 bits of information.
When the “information length=100” is detected, “100 bits” is set as the first predicted value. Therefore, subsequently, while transmission frames storing 100 bits of information are received, the information length of the transmission frame coincides with the first predicted value, it is judged that there is “no error” in step S14, and the “information length=100” is detected. That is to say, during this period, the error detection process is performed only once per transmission frame.
In the above example, the error detection process is performed a total of eleven times while ten transmission frames are received. That is, the error detection process is performed an average of “1.1” times per transmission frame. As a result, the error detection process is performed fewer times when using the BTFD algorithm shown in
Like the algorithm shown in
According to the BTFD algorithm shown in
In step S31, the above counters are reset. The each value of the counter(50), the counter(100) and the counter(200) is set to “0”.
Then, steps S11 through S19 are executed. Steps S11 through S19 have already been described with reference to
In summary, according to the algorithm shown in
In step S32, process B, the value of each counter is checked and the predicted values are arranged in descending order of their respective value. For example, if transmission frames storing 100 bits of information have been received the most, transmission frames storing 50 bits of information has been received less and transmission frames storing 200 bits of information have been received the least, then “100 bits”, “50 bits” and “200 bits” are set in the memory areas x(0), x(1) and x(2), as the first, second and third predicted values, respectively.
In this way, in process B, the information length received most often is written in the memory area x(0) as the first predicted value. On receipt of a transmission frame, an error detection process is performed assuming that an information length of the received transmission frame is equal to the information length which has been detected most often. Therefore, according to this BTFD algorithm, there is a high probability that the information length of a received transmission frame may coincide with the predicted value in the first error detection process (step S14). That is to say, there is a high probability that the information length of a received transmission frame can be detected in the first error detection process in this algorithm. As a result, the total or average number of times the error detection process is executed is reduced.
The above BTFD algorithm is efficient in a communication system where a specific information length is frequently used. For example, if the percentage of frames which store 50 bits of information, 100 bits of information and 200 bits of information are 60 percents, 30 percents and 10 percents, respectively, then “50 bits”, “100 bits” and “200 bits” are set as the first, second and third predicted value, respectively. In this case, on receipt of a transmission frame storing 50 bits of information, the information length is detected in the first error detection process; on receipt of a transmission frame storing 100 bits of information, the information length is detected in the second error detection process; and on receipt of a transmission frame storing 200 bits of information, the information length is detected in the third error detection process. In other words, the probabilities that the information length can be detected by performing one, two and three error detection processes are 60 percents, 30 percents and 10 percents, respectively. In this example, in order to determine the information length of a transmission frame, the average execution time of the error detection process will be as follows.
1×0.6+2×0.3+3×0.1=1.5 times
As a result, the error detection process is executed fewer times when using the BTFD algorithm shown in
Next, the embodiments of the present invention are described. Here, a case where a receiver of a radio communication system adopts the BTFD algorithm of the present invention is used as an example. The communications method is, in this example, assumed to be CDMA using a convolutional code. It is also assumed that 50 bits of information, 100 bits of information and 200 bits of information can be transmitted.
Buffers 1 through 3 store 50 bits of information, 100 bits of information and 200 bits of information, respectively. In other words, information to be transmitted is segmented into units of 50 bits, 100 bits or 200 bits, and is stored in a corresponding buffer.
A control unit 4 gives a selecting instruction to a selector 5 depending on the amount of information stored in each of the buffers 1 through 3 or according to an arrival report from the buffers 1 through 3. This arrival report is information indicating whether each buffer stores information.
The selector 5 selects the data in one of the buffers 1 through 3 according to a selecting instruction from the control unit 4. By this selection, 50 bits of information, 100 bits of information or 200 bits of information is provided for a CRC addition unit 6.
The CRC addition unit 6 appends a CRC to the information selected by the selector 5. It is assumed that the number of bits in a CRC is constant. Since CRC itself is a known technology, the description about it is omitted. A convolutional encoding unit 7 performs the convolutional encoding process on the output of the CRC addition unit 6. A radio unit 8 stores the output of the convolutional encoding unit 7 in a radio frame (frame to be transmitted in a radio network). This radio frame is transmitted through an antenna 9.
If the selector selects 50 bits of information, CRC of 10 bits is appended to the information and the information is encoded, resulting in 120 bits of encoded data. By storing this encoded data in a frame, a radio frame 11 is generated. Similarly, if 100 bits of information are selected, 220 bits of encoded data are generated, and by storing the encoded data in a frame, a radio frame 12 is generated. In addition, if 200 bits of information are selected, 420 bits of encoded data are generated, and by storing the encoded data in a frame, a radio frame 13 is generated.
An antenna 21 receives radio signals. Then, a radio unit 22 terminates the radio frame.
A control unit 23 predicts the information length of the radio frame and provides the predicted value to a Viterbi decoder 24. The control unit 23 also judges whether a next predicted value should be provided to the Viterbi decoder 24, based on the detection result of a CRC error detection unit 25.
The Viterbi decoder 24 regenerates or extracts encoded data from the radio frames using the predicted value provided by the control unit 23 and decodes the encoded data. The CRC error detection unit 25 performs the CRC operation on the data decoded by the Viterbi decoder 24 and judges whether there is an error. This detection result is provided to the control unit 23.
If no error is detected in the CRC operation, the control unit 23 outputs the decoded data obtained by the Viterbi decoder 24 as information bits transmitted by the transmitter. If an error is detected in the CRC operation, the control unit 23 provides a next predicted value to the Viterbi decoder 24.
The operation of this receiver is described below. As described with reference to
On receipt of the first predicted value, the Viterbi decoder 24 regenerates/extracts N bits of data from the received radio frame, where “N” corresponds to the predicted value. For example, if “50 bits” is provided as the first predicted value, 120 bits of data are extracted from the radio frame. The receiver recognizes that the CRC is 10 bits and the encoding ratio in the transmitter is “1:2”.
Then, the Viterbi decoder 24 decodes the extracted 120 bits of data, and then the CRC operation is performed on the decoded data. At this time, if the radio unit 22 receives the radio frame 11 shown in
On the other hand, when the radio unit 22 receives the radio frame 12 or 13 shown in
On receipt of this notice, the control unit 23 provides the second predicted value to the Viterbi decoder 24. Then, the Viterbi decoder 24 regenerates/extracts N bits of data from the radio frame, where N corresponds to the second predicted value. For example, if “100 bits” is provided as the second predicted value, 220 bits of data are regenerated/extracted from the radio frame, and if “200 bits” is provided as the second predicted value, 420 bits of data are regenerated/extracted from the radio frame. Any subsequent operation is basically the same as the operation in the case where the first predicted value is provided.
When these processes detect the information length of the radio frame, the control unit 23 updates the first through third predicted values based on the detection result. For example, if the method shown in the flowchart in
Next, specific embodiments are described.
In the first embodiment, the information length of a received radio frame is set as the first predicted value in a process for detecting the information length of the next radio frame. In other words, on receipt of a radio frame, first, the information length detection process is performed assuming that the information length of a current radio frame is the same as the information length of the previous radio frame. Then, if the trial fails, another predicted value is used.
Specifically, according to the algorithm of the first embodiment, steps S42 and 43 are executed as step S20 (process A) shown in
If no error is detected in an error detection process using the first predicted value (no error in step 14), then the flow returns to step S12 without updating the first through third predicted values, and waits for the next radio frame.
If an error is detected in an error detection process using the first predicted value (error in step 14), then in step S41, the first predicted value is stored in a register y; and then the error detection process is executed using the second predicted value in steps S15 and S16. At this time, if no error is detected in the error detection process using the second predicted value (no error in step S16), it is judged that the information length of the radio frame coincides with the second predicted value and the flow proceeds to step S42.
In step S42, the second predicted value used in step S16 is set as the first predicted value for the next radio frame. Specifically, the second predicted value currently stored in the memory area x(1) is written in the memory area x(0) which stores the first predicted value. And, the first predicted value stored in the register y is written in the memory area x(1) which stores the second predicted value.
If an error is detected in the error detection process using the second predicted value (error in step S16), then the error detection process is executed using the third predicted value in steps S17 and S18. At this time, if no error is detected in the error detection process using the third predicted value (no error in step S18), it is judged that the information length of the radio frame coincides with the third predicted value and the flow proceeds to step S43.
In step S43, the third predicted value used in step S18 is set as the first predicted value for the next radio frame. Specifically, the third predicted value currently stored in the memory area x(2) is written in the memory area x(0) which stores the first predicted value, and the first predicted value stored in the register y is written in the memory area x(2) which stores the third predicted value.
If an error is detected in each of the error detection processes (steps S14, S16 and S18), then an error handling process is performed in step S19, and the flow returns to step S11. Specifically, in this first embodiment, if the information length of a received radio frame is not detected, the error detection process for the subsequent radio frame is performed using the initial setting.
A specific example is described below. In the following description, it is assumed that “50 bits”, “100 bits” and “200 bits” are set in the memory areas x(0) for the first predicted value, the memory area x(1) for the second predicted value and the memory area x(2) for the third predicted value provided in the control unit 23, respectively, by the process in step S11.
Case 1: Consecutively receiving frames storing 100 bits of information, after consecutively receiving a prescribed number of frames storing 50 bits of information.
In this case, while consecutively receiving frames storing 50 bits of information, no error is detected in the error detection process using the first predicted value (50 bits). Specifically, “no error” is detected in step S14, and neither step S16 nor S18 is executed. Therefore, the memory areas x(0) through x(2) are not updated, and the respective states shown in
Then, when a frame storing 100 bits of information is received, no error is detected in the error detection process using the second predicted value (100 bits). Specifically, “no error” is detected in step S16, and step S42 is executed. In step 42, as described above, currently used second predicted value is written in the memory area x(0), and currently used first predicted value is written in the memory area(1). As a result, the memory areas x(0) through x(2) become the respective states shown in
Then, while consecutively receiving frames storing 100 bits of information, no error is detected in the error detection process using the first predicted value (100 bits) Specifically, “no error” is detected in step S14, and neither step S16 nor S18 is executed. Therefore, the memory areas x(0) through x(2) are not updated, and the respective states shown in
Case 2: Consecutively receiving frames storing 200 bits of information, after consecutively receiving a prescribed number of frames storing 50 bits of information.
In this case, the operations performed while consecutively receiving frames storing 50 bits of information is the same as the operations in case 1. On receipt of a frame storing 200 bits of information, no error is detected in the error detection process using the third predicted value (200 bits). Specifically, “no error” is detected in step S18, and step S43 is executed. In step S43, as described above, currently used third predicted value is written in the memory area x(0), and currently used first predicted value is written in the memory area x(2). As a result, the memory areas x(0) through x(2) hold respective states shown in
Then, while consecutively receiving frames storing 200 bits of information, no error is detected in the error detection process using the first predicted value (200 bits). Specifically, “no error” is detected in step S14, and neither step S16 nor S18 is executed. Therefore, the memory areas x(0) through x(2) are not updated, and the respective states shown in
Here, the error detection process is described with reference to
In step S51, the predicted value provided by the control unit 23 is obtained. Specifically, if the flowchart shown in
In steps S52 and S53, N bits of data are regenerated/extracted from the received frame, where “N” corresponds to a predicted value obtained in step S51, and Viterbi decoding is performed on the data. Here, “N bits corresponds to a predicted value” has already been described with reference to
In step S54, a data string is regenerated based on the path selected in step S53. Then, in step S55, the CRC operation on the data string obtained in step S54 is performed. In this CRC operation, for example, a remainder is calculated by dividing the data string obtained in step S54 by a prescribed generation polynomial.
In step S56, the presence of an error is determined based on the result of the CRC operation. Generally, if the remainder of the division is zero, it is judged that there is “no error”. If the remainder is non-zero, it is judged that there is an “error”. If an error is detected, an error signal is outputted in step S57. On the other hand, if no error is detected, a non-error signal is outputted in step S58.
In the first embodiment described above, if the information length of a received radio frame cannot be detected, an error handling process is performed and the flow returns to step S11. However, in the second embodiment, if the information length of a received radio frame cannot be detected, an error handling process is performed and the flow returns to step S12. In this way, according to the algorithm of the second embodiment, if the information length of an immediately previous frame cannot be detected, the latest information length detected will be used as the first predicted value.
In the third embodiment, the number of detections is checked for each information length of a radio frame, and the information length with the greatest number of detections is used as the first predicted value. For example, if 100 bits of information is frequently used and both information lengths of 50 bits and of 200 bits are not used as often, “100 bits” is set as the first predicted value. Then, on receipt of a radio frame, an error detection process is performed assuming that the frame stores 100 bits of information. If an error is detected in the error detection process, the error detection process is repeated using the second and/or third predicted values.
Specifically, according to the algorithm of the third embodiment, steps S54 and S56 are executed as step S32 (process B) shown in
In step S54 (process C), the following process is performed.
In step S56 (process D), the following process is performed.
A specific example of the operation of the third embodiment is described below. In the following description, it is assumed that the counter(50), the counter(100), and the counter(200), and the memory areas x(0) through x(2) are in the respective states shown in
Case 1: When receiving a frame storing 50 bits of information at the state shown in
In this case, since the information length of a received frame coincides with the first predicted value stored in the memory area x(0) (no error in step S14), the counter(50) is incremented in step S52. As a result, each of the counters and each of the memory areas go to the respective states shown in
Case 2: When receiving five consecutive frames storing 100 bits of information in the state shown in
In this case, since the information length of each received frame coincides with the second predicted value stored in the memory area x(1) (no error in step S16), in step S53, the counter(100) is incremented every time one of these frames is received. As a result, each of the counters goes to the respective state shown in
Case 3: When receiving ten consecutive frames storing 200 bits of information in the state shown in
In this case, since the information length of each received frame coincides with the third predicted value stored in the memory area x(2) (no error in step S18), the counter(200) is incremented every time one of these frames is received in step S55. As a result, each of the counters goes to the respective state shown in FIG. 14D. Then, in step S56, the counters(100) and(200) are compared. In this case, since the value of the counter(200) is greater than that of the counter(100), “200 bits” is written in the memory area x(1) for the second predicted value, and “100 bits” is written in the memory area x(2) for the third predicted value. Then, the counters(50) and the counter(200) are compared. In this case, since the value of the counter(200) is greater than that of the counter(50), “200 bits” is written in the memory area x(0) for the first predicted value, and “50 bits” is written in the memory area x(1) for the second predicted value. As a result, each of the memory areas goes to the respective state shown in
After the memory areas x(0) through x(2) are updated in this way, an error detection process is performed according to the updated content.
In this way, according to the algorithm of the third embodiment, the order of the predicted values to be used in the error detection process is determined based on the numbers of detections of information lengths of 50 bits, 100 bits and 200 bits.
In order to implement the operation described above, every time the information length of a received frame is detected, a corresponding counter is incremented (steps S52, S53 and S55). In this case, if the information length is detected in an error detection process using the first predicted value, the first through third predicted values for the next frame are not modified. If the information length is detected in the error detection process using the second predicted value, the detected information length is set as the first predicted value for the next frame by executing step S42. Furthermore, if the information length is detected in the error detection process using the third predicted value, step S57 is executed. In step S57, the following process is performed.
x(0)=x(2)
Specifically, in step S57, first, the detected information length of the relevant frame is set as the first predicted value for the next frame. The second and third predicted values are determined based on the past detection frequency.
As described above, according to the BTFD algorithm of the present invention, the information length of the relevant frame is predicted based on the information length of an immediately previous frame or past frames, and the information length of the relevant frame is detected using the predicted value. Therefore, in a communication system that has a specific tendency to use identical information length, the probability that the prediction described above is correct will be improved, and the number of times that the error detection process is executed will be reduced. As a result, the time needed for a receiver to process a radio frame is reduced and the power consumption of the receiver is also reduced.
According to the BTFD algorithm of the embodiments described above, in a case where a plurality of pieces of information with identical length are consecutively transmitted or in a case where information with a specific length is frequently transmitted, efficiency is improved. Therefore, if a transmitter can implement such data transmission function, the efficiency of a receiver will be further improved.
Instep S61, the initial values ofa first selection value x(0), a second selection value x(1) and a third selection value x(2) are set. In the example of
In step S62, a buffer corresponding to the first selection value is checked to see whether it stores information. If information is stored in the buffer corresponding to the first selection value, then the information is read from the buffer and is outputted in step S63. On the other hand, if the buffer corresponding to the first selection value does not store information, the first selection value is stored in a register y in step S64.
In step S65, a buffer corresponding to the second selection value is checked to see whether it stores information. If information is stored in the buffer corresponding to the second selection value, the information is read from the buffer and is outputted in step S66. Then, in step S67, the second selection value used in the relevant selection process is set as the first selection value in the next process.
Similarly, in step S68, a buffer corresponding to the third selection value is checked to see whether it stores information. If information is stored in the buffer corresponding to the third selection value, the information is read from the buffer and is outputted in step S69. Then, in step S70, the third selection value used in the relevant selection process is set as the first selection value in the next process.
If no buffer stores information, the first though third selection values are initialized again by executing step S61.
By this procedure, frames with identical information length can be consecutively transmitted as much as possible.
In the method of this embodiment, the number of times each information length is used in a transmission is monitored, and frames with the information length transmitted most are selected with priority. In order to implement this operation, a counter corresponding to the information length is incremented every time a transmitter transmit a frame (steps S83, S84, and S86). In addition, when a frame is transmitted according to the second selection values, then step S85 (process F) is executed, and when a frame is transmitted according to the third selection values, then step S87 (process G) is executed.
Process F is basically the same as process C shown in
In the method of this embodiment, a plurality of frames with identical information length are consecutively transmitted as much as possible. After all the frames with identical information length are transmitted, frames with the information length transmitted more frequently are selected with priority. In order to implement this operation, step S91 is executed when a frame is transmitted according to the second selection value, and step S92 (process H) is executed when a frame is transmitted according to the third selection value.
The process in step S91 is basically the same as that in step S42 shown in
As described above, in the communication system of this embodiment, since a procedure for determining an information length in a transmitter and a procedure for predicting the information length in a receiver can be made the same, there is a higher probability that the prediction for the information length of a transmission frame is correct in the receiver. As a result, the number of times that the error detection process is performed in a receiver is reduced and therefore the power consumption of the receiver is also reduced.
Next, an embodiment in a case where the BTFD algorithm of the present invention is applied to W-CDMA is described.
According to the standardized rating of W-CDMA, BTFD may be applied to the following three communications.
Upward communications
Downward communications (DTX indication with Fix position)
Downward communications (DTX indication with Flexible position)
Here, “upward communications” represent signal transmissions from a mobile station to a base station or an exchange station. “Downward communications” represent signal transmissions from a base station or an exchange station to a mobile station.
It is downward communications (DTX indication with Fix position) out of the three communications that the present invention can be applied to easily and practically. Therefore, here an embodiment is described to which the downward communications (DTX indication with Fixed position) of W-CDMA is applied. In addition, in the following embodiment, a case where audio data is transmitted is assumed.
It is assumed that audio data is transmitted in one of the nine communications modes shown in
In each of the communication modes, information in class A through class C is transmitted. Information in class A is information with top priority, and the information is needed in all communications except several exceptions. Information in class B is information with the second priority next to information in class A, and the information is needed when transmitting audio data. Information in class C is information with the lowest priority, and the information is used to improve quality of voice.
As shown in
The operation of a transmitter is described with reference to
Then, if necessary, a rate matching process and a DTX addition process are performed on the data in each class. These processes set the number of data bits in each class to a predetermined value (292 bits, 322 bits and 132 bits for classes A, B and C, respectively) Furthermore, an interleaving process is performed on each class. Here, interleaving process is a process that sorts bits according to a prescribed rule (randomization process). Then, data in each class are segmented into the respective predetermined number of bits.
The interleaving process is performed on each of the data blocks, then each block is segmented into 15 blocks, and finally each of the resulting 15 blocks is stored in the corresponding slot of a radio frame.
As shown in
As described above, when audio data is transmitted in mode “AMR 12.2”, the transmitter generates radio frames in the procedure shown in
In mode “SID-UPDATE”, only 35 bits of class A data are transmitted as audio data. Since the transmission of the control data in mode “SID-UPDATE” is basically the same as the transmission of the control data in mode “AMR 12.2”, the description is omitted.
CRC and tail bits are appended to the 35 bits of class A data and the data is encoded. Through this encoding process, the number of data bits becomes 165. Then, in the rate matching process and the DTX addition process, a prescribed number of bits are appended/deleted to/from the encoded data, and by appending DTX, a data block of 292 bits is generated. Then, the interleaving process and the segmentation process are performed on the data.
As shown in
As described above, a transmitter can transmit audio data while changing communication modes from time to time. In this embodiment, nine communication modes are provided. The amount of information transmitted from a transmitter to a receiver varies depending on the communication mode. For example, in mode “AMR 12.2”, 81 bits of class A data are transmitted in each radio frame, while in mode “SID-UPDATE”, 35 bits of class A data are transmitted in each radio frame.
However, when the transmitter transmits radio frames to the receiver, the communication mode and the number of bits in each class is not reported to the receiver. This notification is possible using the TFCI area of the radio frame shown in
On receipt of a radio frame, the receiver reverses the assembly procedure executed in a corresponding transmitter, as shown in
Then, the receiver detects the information length in class A using the BTFD algorithm of the present invention. In the system of this embodiment, as shown in
An embodiment is described below. Here, it is assumed that “81 bits” is set as the first predicted value. When performing an error detection process using “81 bits” as a predicted value, the receiver performs a decoding process assuming that the transmitter encodes audio data in mode “AMR 12.2”. Specifically, in this case, as shown in
If an error is not detected in this CRC operation, the receiver outputs the resulting 81 bits as information in class A. Here, if there are 81 bits of information in class A, the bit length of class B and that of class C are uniquely recognized to be “103 bits” and “60 bits”, respectively. Therefore, 103 bits of information in class B are reproduced by performing a decoding process which assumes that the transmitter has encoded 103 bits of information in class B. Likewise, 60 bits of information in class C are reproduced by performing a decoding process which assumes that the transmitter has encoded 60 bits of information in class C.
On the other hand, if the CRC operation detects an error on the 93 bits, the process described above is repeated using the second predicted value. In this embodiment, “35 bits” is set as the second predicted value. When performing an error detection process using “35 bits” as the predicted value, the receiver performs a decoding process assuming that the transmitter has encoded audio data in mode “SID-UPDATE”. Specifically, in this case, as shown in
If an error is not detected in this CRC operation, the receiver outputs 35 bits obtained by deleting the CRC from the 47 bits as information in class A. Here, in a case where the information in class A is 35 bits, there is no information in class B and class C.
On the other hand, if the CRC operation detects an error in the 47 bits, the process described above is repeated using the third, fourth, fifth predicted values and so on, until the information length of the radio frame is detected.
In this embodiment described above, the first through ninth predicted values are determined by the algorithm of the present invention. For example, according to the algorithm shown in
In this embodiment described above, since the communication mode is uniquely correspond to the information length of class A data, the communication mode can be uniquely recognized by detecting the information length of the class A data, when the information length is detected using the BTFD algorithm of the present invention. Therefore, it is correct to say that the communication mode or a transmission format specified in the communication mode can substantially be detected by performing the BTFD algorithm in this embodiment.
Although only the first through fourth embodiments of the BTFD algorithm of the present invention are shown, the present invention is not limited to these embodiments. Specifically, for example, when detecting the information length of a received frame, a CRC operation can be performed using the information length detected in a previous frame, and if the CRC operation detects an error, the BTFD algorithm described in the “3G TS 25.212 version 3.1.0” can be executed. Alternatively, the average number of times the error detection processes is executed per frame is monitored while executing the algorithm of the first embodiment, and the algorithm can be automatically switched over to one of the second through fourth embodiments when the average value exceeds a prescribed value.
Although CDMA is adopted, in the embodiments described above, the present invention is not limited to CDMA. The present invention is widely applicable to a method for detecting the information length of a frame or the transmission format of the frame in a communication system which transmits frames of information.
Obuchi, Kazuhisa, Yano, Tetsuya, Uchishima, Makoto
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